Heritabilities and genetic and phenotypic correlations of litter uniformity and litter size in Large White sows

Litter uniformity, which is usually represented by within-litter weight coefficient of variation at birth （CVB）, could influence litter performance of sows and the profitability of pig enterprises. The objective of this study was to characterize CVB and its effect on other reproductive traits in Large White sows. Genetic parameters and genetic correlation of the reproductive traits, including CVB, within-litter weight coefficient of variation at three weeks （CVT）, total number born （TNB）, number born alive （NBA）, number born dead （NBD）, gestation length （GL）, piglet mortality at birth （Mo）, piglet mortality at three weeks （M3）, total litter weight at birth （TLW0）, and total litter weight at three weeks （TLW3） were estimated for 2 032 Large White litters. The effects of parity and classified litter size on CVB, CVT, TNB, NBA, NBD, GL, M0, M3, TLW0, and TLW3 were also estimated. The heritabilities of these reproductive traits ranged from 0.06 to 0.17, with the lowest heritability for CVB and the highest heritability for TLW0. Phenotypic and genetic correlations between these reproductive traits were low to highly positive and negative （ranging from -0.03 to 0.93, and -0.53 to 0.93, respectively）. The genetic correlations between TNB and CVB, and between M0 and CVB were 0.32 and 0.29, respectively. In addition, CVB was significantly influenced by parity and litter size class （P〈0.05）. All the results suggest that piglet uniformity should be maintained in pig production practices and pig breeding programs.